The Glory Hole is Lake Berryessa's spillway. When the North Bay gets lots of rain, the Napa County reservoir fills and water starts to spill into the hole. The drain isn't at the bottom of the tub. It's located near the top.
When the lake swells, water falls into the eight-foot-wide pipe that dumps excess water 200 feet into Putah Creek.
The last time this reservoir overflowed was in February 2017, in the middle of another especially wet winter that caused widespread flooding and damage. Before that, it had been 10 years.
Check out the amazing photo below of what it looked like on Tuesday evening!